One of the most exacting applications of platinum is in the production of glass fibers. Molten glass often at temperatures ranging from 1200.degree. to 1600.degree. C. passes through a series of orifices in a bushing made of platinum or platinum alloy. Advances in glass fiber production are demanding both larger bushings and higher operating temperatures, which, in turn, places even more of a demand on the alloy used to make the bushing.
Alloys for these operations may be produced by dispersing very small, hard particles called dispersoids into the alloys to improve the strength of their microstructure. These system are known as dispersion-strengthened metals and alloys. Dispersion strengthening is mechanical alloying which uses a high energy ball mill to achieve the intimate mechanical mixing typical of the process. An attritor mill or vibratory mill may be used.
In order to more easily mechanically alloy the metal or alloy, it is desirable to begin with a finely powdered material. One method for atomization of the metal is to impinge a stream of molten metal with a stream of a fluid such as water. The result is a finely powdered metal or alloy which may be mechanically alloyed with an appropriate despersoid.
One means for providing a stream of molten material for atomization is a container with an orifice in the bottom. This means has its limitations as there is no means for stopping the flow of molten material once processing begins. Advances have provided a stopper or plunger for controlling the flow of molten material through the orifice. The stoppers or plungers usually are made of ceramic materials. Problems exist with the ceramics in that they can permanently seal the orifice either by bumping during loading of the alloy charge or by reaction between the container and plunger if the molten material is too hot.